Guadiana River Basin (Spain/Portugal)

Hydrology

The headwaters of the Guadiana are one of the driest areas of Europe, with an annual average rainfall of only 415 mm. As a consequence the Guadiana river has an average total runoff of only 90 mm yr-1 (Kilsby et al., 2007).

Surface water

Pressures on surface water include the risk of eutrophication due to high nutrient concentrations from wastewater spills and nitrates from agricultural sources. Additionally the high density of livestock in some of the agricultural regions leads to high concentrations of organic matter. Hydrological alteration of channels, wetlands and lagoons adds additional pressure on both, surface and groundwater resources (Montesinos, 2012).

Groundwater

There are 20 groundwater bodies located in the Spanish part of the Guadiana River Basin and nine in the Portuguese part. 12 out of 20 aquifers are located in the autonomous region of Castilla-La Mancha in Spain. In other words, 74% of the basins groundwater bodies are located in Castilla-La Mancha which corresponds to Guadiana's upper basin (Montesinos, 2012).
However, aquifers in the GRB are subject to overexploitation and annual withdrawals often exceed available resources. Contamination of groundwater bodies with nitrate was found in 14 out of 20 groundwater bodies located in the Spanish part of the basin (Montesions, 2012).

Droughts

Van Loon & Van Lanen, 2012 classify the hydrological droughts in the upper Guadiana catchment. The upper Guadiana basin is the headwater catchment and spans across 16,480 km², making it the largest sub-basin by size. Based on a hydrological model they identify the occurence of wet-to-dry-season droughts in the upper basin. A wet-to-dry-season drought is related to a rainfall deficit in the wet winter season that continues into the dry summer season. Regardless of the precipitation in the wet season, the rain is lost to evapotranspiration. As a result, soil moisture and groundwater stores are not sufficiently recharged during the wet season.

References:

Kilsby, C.G., Tellier, S.S; Fowler, H.J.; Howels, T.R. (2007): Hydrological impacts of climate change on the Tejo and Guadiana Rivers. Hydrology and Earth System Sciences Discussions, European Geosciences Union, 11 (3), pp.1175-1189. hal-00305659

Montesinos, S. (2012): SYSTEM OF ECONOMIC & ENVIRONMENTAL ACCOUNTS FOR WATER IN GUADIANA RIVER BASIN GUASEEAW FINAL REPORT (Technical Part).Available at: https://ec.europa.eu/environment/water/blueprint/pdf/GuaSEEAWreport.pdf

Van Loon, A. F.; Van Lanen, H. A. J. (2012). A process-based typology of hydrological drought. Hydrology and Earth System Sciences, 16(7), 1915–1946. doi:10.5194/hess-16-1915-2012